Leam,
First, please understand I don’t know what your experience level is with using taps and dies. When I began learning these things in 1973, I knew almost nothing about them. So if information I give is something you already know, please understand. Some folks on the forum will know only some of this information or none at all.
flehto said:
I use an #8-32 tang screw and rear lock bolt and a #6-32 front lock bolt. So only 2 tap sizes are needed plus body and tap drills for both sizes.
Fred
Leam, in case you did not know, the reason Fred suggested using the #6-32 for the front lock bolt is that this is a smaller diameter screw that will be easier to fit between the bottom of the barrel and top of the ramrod hole in the stock. You can get lock bolts for both size screws that have the same size heads, so they look better outside the side plate, or you can shape the larger head of the #8-32 screw to match the smaller head of the #6-32. However, some folks don’t worry about the size of heads matching each other. This is up to you, the builder. HOWEVER, if your lock plate is already drilled and tapped for the side plate screws/bolts, then you have to use the size screws that will fit those holes.
BTW, flehto/Fred is a real machinist, so if I inadvertently type something that is wrong, I hope he will correct me. I was trained in some machining to do gun work, but am not a fully qualified machinist like Fred.
From bad experiences, I have learned NOT to trust some of the drill bits that come with taps when you find a combination drill bit and tap sold together in one package in hardware stores. Many times the drill bit provided makes the hole too large to give enough percentage of threads for gun work. The reason for this is “Harry Homeowner” often/usually has no experience drilling and tapping holes, so they provide a drill bit that will only give a 50 ”“ 60 percent amount of threads in the hole, because it is much easier to tap the hole with the larger size drill bit and there is much less of a chance Harry Homeowner will break the tap when threading the hole, because he doesn’t use oil or tries to force the tap without backing it off enough during the tapping process.
For most tapped holes for use in gun work, I prefer a 75 percent thread size in the hole. I am not sure what percentage of threads is recommended for a flash hole liner, though. It may be an 85 percent thread, but I am not sure. Fortunately the folks who sell the flash hole liners usually also sell the correct size drill bit for their flash hole liners.
On the subject of percentage of thread sizes in a hole, I copied this from “MACHINIST’S Practical Guide” from Morse cutting tools. This is a pocket size book my best friend in life (who was a real machinist) gave me back in 1974. I have almost worn the book out since then, primarily looking up tap and drill sizes and fractional conversion to decimal sizes when I often needed that information:
“Tap drill sizes shown are for holes as deep as the diameter of the tap. A 53 percent thread will break the bolt (screw) before it will strip ”“ in most cases. For this size stock (material thickness) use a 75 to 80 percent thread tap drill.
For VERY THIN stock use 100 percent thread tap drill.
A 100 percent thread is only 5 percent stronger than a 75 percent thread, but it requires three times the power to tap.“
When flehto/Fred is talking about “body” drill bits, I am pretty sure he means a drill bit that will drill a hole large enough for the body or shank of the screw/bolt to easily pass through, such as the hole in a side plate for the side plate bolts/screws. This is also known as a clearance drill. A drill bit needs to drill a hole two or three thousandths (or slightly) larger than the body/shank of the screw/bolt to easily pass through the hole. Now, here’s a catch, though. Sometimes you run into screws/bolts that have a body/shank diameter that is a little bit larger than normal for the threads. So it is really a good idea to double check the diameter of the body/shank with a good Dial or Digital Caliper to ensure the drill bit will drill a big enough hole for the bolt/screw to easily pass through.
Something you need to know about “Number Size” drill bits is that the diameter of the drill bit and hole gets SMALLER as the number size goes up. IOW, a Number “1” size drill bit makes a hole .228 inch in size and a Number “80” makes a hole .0135 inch in size.
OK, if I have not yet bored you to tears, GOOD NEWS. Now that you have the above information, it is time for some recommended drill sizes for the two screw sizes.
#6-32
Use Number Size “36” Drill Bit for a hole you are going to tap/thread.
Use Number Size “28” Drill Bit for the minimum size hole you need the body/shank of the screw/bolt to pass through, as in going through the Side Plate.
#8-32
Use Number Size “30” Drill Bit for a hole you are going to tap/thread.
Use Number Size “19” Drill Bit for the minimum size hole you need the body/shank of the screw/bolt to pass through, as in going through the Side Plate.
In case you would like to get a copy of “MACHINIST’S Practical Guide” for yourself, here is a link:
http://www.penntoolco.com/morse-pocket-size-machinist-guides/
Oh, if I have not put you to sleep, there is more info coming in my next post.
Gus